Conductor size for earthing SWA shield to TT system?

Calculate the prospective fault current on the feed cable to the SWA, then use the adiabatic equation to assess the minimum CSA for the earth connection.

Details covered here:

Same size as the cores of the cable and you cannot usually go wrong.

I assume that the only protection you are considering is a spade through the SWA and that it should trip the head end MCB.

Presume you're using an insulated "break" gland at the shed end and the she d is forming a TT system? The RCD operating residual current will be low so the main consideration will be physical resilience hence affected by mecha nical protection arrangements. It used to be tabulated as MINIMUM 2.5mm2 if protected or 4.0mm2 if not protected but other conditions apply if buried in soil/insulated/bare/copper/steel If you haven't got a copy of the curren t wiring regulations or "on site guide" try the local library.

Damn I misread the original post. I took the question as what size conducto r from earth rod to MET in the shed TT system ?

And your answer, if that had been the question, was spot on:-)

Thanks for all the responses - now sorted.